1. Field of the Invention
The present invention relates to a lens apparatus used for television broadcast.
2. Description of the Related Art
In recent years, more sophisticated control has been demanded for a lens system of a television camera used in broadcast, such as an ENG (Electronic News Gathering) camera used in reporting, relaying, dramas, varieties, documentaries, and so on. For satisfaction of such demand, there has been suggested a lens system including a computing device such as a microcomputer (CPU: Central Processing Unit) and controlling the position of a lens. In such a lens system, an encoder is often used instead of a potentiometer, which is a position detector mainly used in a conventional lens, in view of the easiness of processes performed when a microcomputer is used in order to perform position control with higher precision.
For example, U.S. Pat. No. 5,930,054 discloses a technique of detecting a relative position by using a compact and inexpensive incremental encoder and also using an absolute position detector to detect an absolute position, such as a potentiometer. In this case, a datum point can be detected in short time without an influence of backlash or the like, whereby highly-precise lens control can be performed.
On the other hand, U.S. Pat. No. 7,218,849 realizes highly-precise position detection of a lens by automatically initializing an absolute position every time the power is turned on with the use of a relative position detector, such as an optical incremental sensor or a magnetic incremental sensor, and an origin detector. An operation of initializing an absolute position performed by a photographer every time the power is turned on is omitted, so that the photographer can start shooting immediately after power-on, while a highly-precise operation of the lens is realized.
Also, the position of the lens is detected and stored and the absolute position is automatically initialized every power-on with the use of the relative position detector and the origin detector. Then, after the initialization has been completed, the lens is returned to the stored position. In this way, the initialization that is automatically performed after power-on prevents that a picture not intended by the photographer is shown after power-on, so that a highly-precise operation of the lens is realized.
However, in the camera systems according to the related arts, the time from when power is turned on until when an image can be recorded is about 10 seconds. Larger capacity and lower cost of memories in recent years enable the memories to be loaded in television cameras, so that images can be recorded. This type of product is capable of recording images in a memory upon power-on. Therefore, if detection of an origin (i.e. initialization) is performed at a currently-used normal servo drive speed, the lens performs an operation not intended by the photographer and unusable images are recorded for a long time, which should be improved.
Particularly, in iris control, exposure is not accurately controlled without detection of an iris position and thus detection of an origin is necessary. However, an operation of the iris performed at detection of the origin causes unnecessary change in exposure, resulting in inconvenience.
In the techniques according to the above-mentioned patent documents, detection of an origin at power-on is performed at the speed enabling a driving motor to move the lens with an operation by an operating member in the state where the lens apparatus connects to a camera.